CRACK-PROPAGATION BEHAVIOR OF Y-TZP CERAMICS

Y-TZP ceramics present the twofold advantage of a very fine grain size and a phase transformation leading to some reinforcement, making them useful in hip joint head prostheses. The subcritical crack growth of such a material that mainly drives the lifetime of the components has been evaluated for wide crack velocity ranges down to 10(-11) m/s by using both double torsion and static fatigue tests, It appeared that subcritical crack growth was activated by H2O. It is shown that two types of flaws should be considered: surface flaws caused by machining located in the compressive layer present at the surface, and so-called volume flaws, The subcritical crack growth and the toughness of both types of defects are different. The relevance of subcritical crack growth analysis for such surface cracks is discussed, The compressive layer at the surface leads to a threshold value below which no crack growth occurs.